Page 119 - Wastewater Solids Incineration Systems

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the furnace. The signal from the thermocouple is connected to a remote transmitter
or a PLC terminal unit by instrumentation wiring. At least one thermocouple is pro-
vided on each hearth, with multiple thermocouples placed on some hearths,
depending on the furnace control system. A thermocouple is also provided at the
outlet of the incinerator to measure exhaust gas temperature.
Pressure is measured by pressure transmitters through a pressure tap. The trans-
mitter transmits the signal to the control system through instrumentation wiring.
Pressure taps may be short pipes or tubes connected to the furnace wall and the
transmitter, or may be provided with purge air to prevent the pressure taps from
being plugged. Pressure measurements are typically made on some of the lower
hearths and the top hearth or the exhaust air duct.
Oxygen is measured either remotely or by an in-situ oxygen analyzer. Where a
remote oxygen analyzer is provided, a sample of exhaust is withdrawn through a
stainless steel tube and conveyed to the oxygen analyzer system. Oxygen is typically
measured in the exhaust gas duct.

9.4 Furnace Subsystems
The MHF includes several subsystems:

• Dewatered cake conveyance and feed system—this includes belt conveyors,
screw conveyors, dewatered cake pumps, and piping systems.
• Burner fuel system—this includes the burner control system, the fuel valve
and safety trains, pumps, and piping.
• Burner combustion air system—this includes combustion air blowers and
ducting systems.
• Auxiliary combustion air system—this includes fans/blowers and ducting
systems.
• Shaft cooling air system—this includes shaft cooling air fans and ducting.
Subsystems are described in Appendix B.

9.5 Multiple-Hearth Furnace Combustion Enhancements
Several combustion enhancements have been developed for MHFs to assist in
meeting requirements of the 40 CFR Part 503 and other regulations. These include a
patented afterburning system called the RHOX process, flue gas recirculation, and
oxygen injection.